Rated 5 out of 5 stars

This has helped my work immeasurably, especially in combination with Firebug. By cutting the XPath from Firebug into XPath Checker, I can usually play the "what-if" game to see immediate results in the kind of interactive feedback cycles that we've come to take for granted, but that were the fundamental paradigm switch that made spreadsheets so popular and powerful on early computers. Don't take this analogy lightly. The ability to visually choose an item in Firebug, then refine it in XPath Checker is the kind of immediate feedback that makes a huge difference.

This review is for a previous version of the add-on (0.4.1).